This invention relates to a method and device for sealing a filter press-type electrolytic cell, and more particularly, to a combination seal and cover member for an electrolysis cell frame member for example used in a filter press type electrolytic cells.
Electrolytic cells of the filter press-type are known to be used for the electrolysis of aqueous salt solutions and have been commercially employed for the production of chlorine and caustic from brine. The filter press type electrolytic cell for electrolysis of an aqueous salt solution commonly employ a plurality of frame members with electrodes held thereto and assembled in a filter press type arrangement, separated from each other by membranes, diaphragms or microporous separators, forming a plurality of anolyte and catholyte compartments. The electrodes used in the cells are generally either monopolar or bipolar electrodes.
Membranes typically used in the cells are generally available in sheet form and have ion exchange properties, for example, membrane materials employed in the cells are such as those marketed by E. I. duPont de Nemours and Company under the trademark Nafion.RTM. and by Asahi Glass Company Ltd. under the trademark Flemion.RTM..
Typically, a press means is used to compress or clamp together the separators in sheet form between the sides of the frame members of the filter press cell and electrolyte is used to fill the compartments of the cell. To provide a fluid-tight seal between the frame members and the separator without damaging the separator, the electrolytic cells employ substantially flat, solid gaskets having a rectangular cross-sectional area or tubular type gaskets having a circular cross-sectional area made of elastomeric material. One or two gaskets can be used to fit between the cell frame members on a peripheral flange portion of the frame members and on either side of the membrane. While most gaskets can provide a liquid-tight seal the seal is generally not completely fluid-tight, i.e. liquid and gas-tight. To some extent fluid seepage occurs at the interface formed between the membrane contacting the gasket members.
The problem of fluid seepage occurs particularly in cells which employ membrane separators that utilize a support or reinforcement material in the membrane. This reinforcement material is usually used because it provides the normally weak membrane sufficient strength for handling and installing into industrial size membrane filter press electrolytic cells. The problem associated with the use of support or reinforcements in membranes is it allows gases and liquids to seep from the inside of the operating cell to the exterior. This seepage can cause severe damage to the outer surface of the cell peripheral surface. Fluid seepage can also exposes operating personnel to potentially hazardous chemicals. The problem of fluid seepage is aggravated by the use of pressurized cells operating under an internal electrode compartment pressure. The contemporary compression-seal means now being used by industry cannot significantly block the leakage of the liquids and gases in the electrolytic cells.
Another problem associated with the use of conventional gasketing of filter press cells is membrane drying. In a conventional membrane filter press type cell operation, the membrane is usually extended past the periphery of the cell and exposed to the environment. This exposure, in time, allows the membrane to dry and possibly crack. Any cracks formed in the exposed surface of the membrane can propagate, during operation of the cell, through the membrane to the portion of the membrane which is inside the cell, i.e., the operating area of the membrane, which in turn, can cause severe operation problems such as explosions and eventual shutdown of the cell operation.
Still another problem associated with the assembly of filter press cells is attaching the gaskets to the frame member. Heretofore, the cell gaskets were glued or taped to one of the electrode frames prior to assembling to cell elements together. In another method, the cell frames, membranes and gaskets were assembled in the horizontal position to ensure a planar placement of the membrane and gaskets, and thereafter the assembled cell was stood in the upright position for operation. These approaches are unsatisfactory as they present time consuming complex procedures, costly equipment and safety hazards to personnel. These procedures may also allow the membrane to dry and crack thereby rendering it unfit for operation.
It is desired to provide a means suitable for sealing an electrolytic cell to reduce the complexity of assembling the elements of an electrolytic cell.